This invention relates to a method of adjusting the optical axis of an ion beam in a focused ion beam apparatus and to a focused ion beam apparatus.
Conventionally, for example like the apparatus introduced in the literature Submicron Working Using Focused Ion Beam (SSD 81-76)' (Electronic Communications Society Research Group, Dec. 21, 1981), focused ion beam apparatuses have been known which, after constricting an ion beam produced from a liquid metal ion source such as Gallium with a fixed stop, to obtain beam current and diameter over a wide range, constrict the ion beam further by means of a stop having a plurality of different openings and made so that it is possible to select these arbitrarily, focus it into a spot shape with an objective lens, raster scan radiate it using a scanning electrode and carry out working of a sample surface. Also, they are provided with an image display device for displaying a pattern of the sample surface on the basis of the plane strength distribution of secondary charged particles emitted from the sample surface irradiated with the ion beam.
In this kind of focused ion beam apparatus, to make it fully exhibit its performance, it is considered necessary to make it so that the ion beam passes through the centers of ion optical system parts such as a stop, a lens and a deflecting electrode. To achieve this, the performance as an apparatus has been realized by performing highly accurate machining in making the parts and paying close attention to assembly.
However, because the ion source is consumed with use of the focused ion beam apparatus, it is necessary to replace it when required, but at the time of replacement the ion beam produced from the new ion source does not always pass through the centers of the ion optical system parts. Because of this, it is necessary to adjust the position of the ion beam so that it passes through the centers of the ion optical system parts.
Also, because a stop having a plurality of different openings and made so that these can be selected arbitrarily wears and stains with use of the focused ion beam apparatus, it must be replaced periodically. At the time of this replacement, because a position misalignment between the center of the new stop and the ion beam arises, it is necessary to carry out that adjustment.
That is, conventionally, when the ion source has been replaced, for example as shown in the apparatus described in Japanese Unexamined Patent Publication No. H.3-29249, the ion source is mounted on an X-Y stage and the position of the ion source is adjusted by driving this X-Y stage. However, in this case, the position misalignment is adjusted with the ion source attachment position being checked visually with a CRT monitor, and there is no mention of a method with which it is possible to determine that the ion beam produced from the ion source is passing through the centers of the ion source optical system parts. Also, as another example, as described in Japanese Unexamined Utility Model Publication No. S.59-47960, there is an apparatus wherein a second anode part is provided movably in a horizontal direction and a driving mechanism for driving this second anode part in the horizontal direction is provided. This is an apparatus relating to an electron gun, but it can also be utilized in relation to an ion source. However, in this example also, there is no mention relating to how it is possible to determine that the beam is passing through the centers of the optical system parts.
Consequently, conventionally, adjustment of position has been realized by making it converge on the target position by carrying out the operation repeatedly, and the degree of achievement of that adjustment and the time required for the operation depend on the skill of the worker. Also, because the parameters relating to the adjustment have not been quantified, it cannot be carried out automated with a computer.
As one solution method for this kind of position adjustment, there is the method described in Japanese Unexamined Patent Publication No. S.61-88437. However, because due to the fact that the structure thereof is complex and that there are multiple transmission holes the ion beam and secondarily produced particles pass through these multiple transmission holes and become noise components, it becomes difficult to realize the performance of image quality and resolving power and the like sought in a focused ion beam apparatus.
On the other hand, the effect of using a stop having a plurality of different openings is shown in the above-mentioned literature Submicron Working Using Focused Ion Beam', and also, in connection with a method of selecting an optimum opening from the different openings, one is described in Japanese Unexamined Patent Publication No. H.3-163741, but a method for aligning the center of the opening with the ion beam is not mentioned in either. Therefore, like the position adjustment of the ion source, because the position adjustment is realized by making it converge on the target position by carrying out the operation repeatedly, the degree of achievement of that adjustment and the time required for the operation depend on the skill of the worker. Also, because the parameters relating to the adjustment have not been quantified, it cannot be carried out automated with a computer.